Which requirements must be fulfilled before coupling a semi-trailer?

You answered correctly. Before coupling a semi-trailer, it is necessary that the fifth wheel is unlocked and opened so that the trailer kingpin can be properly inserted. The height of the fifth wheel and the trailer coupling must also be roughly the same so that coupling can happen smoothly and safely—this prevents damage and ensures everything lines up as needed. Tube and cable connections must only be made after the trailer is securely coupled, not before. This order helps prevent damage and ensures correct operation. Remembering this sequence will help you answer similar questions about coupling procedures in the future.